Process control valves are commonly used in fluid handling systems and fluid delivery systems to manipulate the flow of a fluid. In general, a process control valve may regulate flow by selectively allowing fluid to reach a destination or inhibiting fluid from reaching a destination. The fluid pressures associated with the systems often affect the operation of the valves. For example, valves may be opened or closed to manipulate the pressure at different points or stages of a process. In other examples, the operation of a valve may depend on pressure values at defined points in the system.
In process control systems involving gaseous agents, the process control valve may include a pressure relief valve designed to vent gases to the atmosphere during certain overpressure conditions. In some situations, the process control may malfunction and cause gases to be vented to the atmosphere.
Because the exact valve position or valve status (e.g., whether the valve is open, closed, in a bleed mode) is not always clear to an operator, a valve may be releasing gases without the operator's knowledge. These so-called fugitive emissions can negatively affect processing efficiency. The fugitive emissions may also present public health and safety risks, particularly to those in the vicinity of the process control system. Because of the public health risks, government regulatory bodies, for example the United States Environmental Protection Agency (EPA), may regulate the emission of such gases. As such, a process control system operator may be fined by a regulatory body for releasing gases, where the fine is typically based on the volume of fugitive emissions vented to the atmosphere. Therefore, while fugitive emissions are common in many processing applications, they do present unique problems for process control system operators.
To help address fugitive emissions, operators typically employ manual methods (e.g., manual inspections of the valve) to control or monitor valve operation. The effectiveness of such inspections, however, depends on the frequency of operator inspection and the accuracy with which the valve is checked. Any error could lead to considerable fugitive emissions without operator knowledge, which could further lead to substantial fines.
Process control system operators are typically fined based on a calculated volume of gases vented to the atmosphere. Calculating the actual volume of fugitive emissions is difficult; and therefore regulatory bodies apply worst-case scenario assumptions to the calculation, namely assuming a maximum flow rate of emissions over the entire time period between inspections, until the emissions have been shown to have stopped.
This worst-case scenario calculation can be extremely costly for an operator, because in practice fugitive emission releases are often brief, occurring between inspection cycles. Unfortunately, without information on emission flow rates, valve position, and valve release times, accurately calculating fugitive emissions data, to counter the determinations of the regulatory body, is not feasible. Therefore, there exists a need in the art for techniques to help operators detect fugitive emissions and more accurately quantify the amount of emissions.